1. Field of the Invention
The present invention relates to a piezoelectric vibrator, a manufacturing method thereof, and an oscillator, an electronic equipment or a radio clock which includes the piezoelectric vibrator.
2. Description of the Related Art
In mobile phones and personal information terminal equipments, a large number of piezoelectric vibrators are used as timing sources of control signals, reference signal sources, clock sources and the like. A large number of structures of the piezoelectric vibrators adopt a mode in which a vibrator piece is fixedly secured in the inside of a base formed of a box-like ceramic package using a conductive adhesive agent or a mode in which a vibrator piece is fixedly secured in the inside of a hermetic vessel of a cylinder type by solder plating. Along with the further miniaturization of the vibrator, it becomes difficult to accurately mount a vibrator piece on a holder such as a base or a plug made of ceramic. As an example of means which has possibility of solving this drawback, there has been known a piezoelectric vibrator which includes a frame (see Japanese Patent Laid-open 2000-223995, for example).
A specific example of surface-mount-type piezoelectric vibrator which has a frame provided with bonding films on front and back surfaces and bonds the frame, a lid and a base to each other is explained hereinafter in conjunction with drawings.
FIG. 6 is an exploded perspective view showing constitutional members of the surface-mount-type piezoelectric vibrator. In FIG. 6, the piezoelectric vibrator includes a frame 2 which is connected with one end of a vibrator piece 1 and is integrally formed in a state that the frame 2 surrounds the vibrator piece. Bonding films not shown in the drawing are formed on front and back surfaces of the frame 2. To the front surface side of the frame 2, a lid 6 having a first recessed portion 4 in a portion which faces the vibrator piece 1 is bonded by way of the bonding film. On four ridge portions of non-bonding surface side of the lid 6, beveling portions 15 are formed. To the back surface side of the frame 2 on a side opposite to the lid 6, a base 7 having a second recessed portion 5 on a portion which faces the vibrator piece 1 is bonded by way of the bonding film. The base 7 includes external terminal connecting portions 17 where external electrode films not shown in the drawing are formed at four corners thereof. Further, beveling portions similar to the beveling portions of the lid 6 are formed on four ridge portions on a non-bonding surface side of the base 7.
A manufacturing method of the piezoelectric vibrator having the above-mentioned constitution is explained simply using a flow of manufacturing steps shown in FIG. 10. A piezoelectric wafer which constitutes a first wafer is formed by cutting crystal in the rough, polishing the cut crystal to a given thickness and cleaning the polished crystal (step 50). Thereafter, a plurality of vibrator pieces which include exciting electrode films are formed on the wafer by chemical treatment such as etching. On front and back surfaces of a frame which is integrally connected to one ends of the vibrator pieces and surrounds peripheries of the vibrator pieces, bonding films are formed using a metal film made of aluminum, for example (step 51).
A second wafer (hereinafter referred to as “lid wafer”) is polished to a given thickness and, thereafter, is cleaned, and an uppermost surface layer which is degenerated by machining is removed by etching or the like (step 60). Next, a first recessed portion is formed in a state that the mechanical deformation attributed to the vibration of the vibrator piece is not obstructed (step 61).
A third wafer (hereinafter referred to as “base wafer”) is, in the same manner as the lid wafer, polished to a given thickness and, thereafter, is cleaned, and is etched (step 70). Subsequently, a second recessed portion is formed in a state that the mechanical deformation attributed to the vibration of the vibrator piece is not obstructed (step 71). Further, through holes (penetrated holes) for forming external electrodes are formed in the base wafer (step 72).
Three wafers which are prepared in the above-mentioned manner are aligned to given positions in accordance with reference marks which are formed on the respective wafers (step 80). A state in which three wafers are aligned with each other is shown in FIG. 11. As shown in FIG. 11, the first piezoelectric wafer 8 is configured to be sandwiched between the lid wafer 9 and the base wafer 10. Here, numeral 16 depicted by a broken line indicates through holes which are formed in step 72. Three wafers overlapped to each other are bonded using an anode bonding device (step 81). Subsequently, after bonding, grooves of a given size having a V-shaped cross section are formed in a surface side (non-contact surface side) of the base wafer using a dicing saw or the like (step 82). Here, the V-shaped groove forming is referred to as the bevel cutting.
Next, on the base wafer side, a metal thin film is formed on external terminal portions (step 83). Thereafter, the wafer is again set on the dicing saw or the like and is cut into individual piezoelectric vibrators (step 84). Here, the step in which a plurality of piezoelectric vibrators which are formed on the wafer are individually cut and separated is referred to as the full cutting. The individually separated piezoelectric vibrators are individually subjected to the frequency trimming, wherein the piezoelectric vibrators are trimmed to a given frequency (step 85). Finally, a corrosion resist film is applied to an outer surface of a housing of the piezoelectric vibrator by coating except for a terminal surface thus completing the piezoelectric vibrator (step 86). Here, although the portion where the through hole is formed in the wafer stage is divided in four by full cutting, the divided portion is referred to as an external terminal connecting portion. This portion is indicated by numeral 17 in the above-mentioned FIG. 6.